1. Field of the Invention
The present invention relates to a buffer tank for an inkjet printer wherein the buffer tank is provided on a carriage movable for printing, and also relates to an inkjet printer.
2. Discussion of Related Art
There has conventionally been known an inkjet printer including a carriage that is movable along a recording medium such as a recording sheet, and an inkjet recording head and a buffer tank both of which are provided on the carriage. The inkjet recording head has a plurality of groups of nozzles, and ejects, from each group of nozzles, a corresponding one of a plurality of sorts of inks so as to record an image such as characters, symbols, etc. on the recording medium. The buffer tank has a plurality of delivery chambers that store the plurality of sorts of inks, respectively, that are supplied from a plurality of ink storage tanks, respectively, that are not provided on the carriage, i.e., are detachably attached to a tank supporter independent of the carriage.
The buffer tank is provided in respective ink supply passages between the ink storage tanks and the inkjet recording head, and has a plurality of ink inlets to receive the plurality of sorts of inks, respectively, and a plurality of ink outlets to output those sorts of inks, respectively. The buffer tank, provided on the movable carriage, temporarily stores the inks supplied from the ink storage tanks, and functions as a damper or buffer that damps or buffers, i.e., absorbs the changes of pressure of the inks that occur when the carriage is moved.
The inkjet recording head includes a sheet-type piezoelectric actuator that selectively applies an appropriate pressure to an arbitrary one of a plurality of pressure chambers communicating with a plurality of nozzles, respectively, so that the nozzle communicating with the one pressure chamber ejects a droplet of ink at a speed and an amount that correspond to the applied pressure, and thereby records or prints an image on the recording medium.
Thus, the stable ink-ejecting characteristic of the inkjet recording head and the excellent printing performance of the inkjet printer can be maintained by damping or absorbing the pressure changes of the inks and applying the appropriate ejecting pressure to the inks.
The ink storage tanks and the ink inlets of the buffer tank are connected by a plurality of ink supply tubes, respectively. When the carriage is moved and returned during a printing operation, an acceleration is applied to the inks present in the ink supply tubes and/or the buffer tank provided on the carriage, so that the pressure changes of inks occur.
Generally, a damper is used to absorb the above-indicated pressure changes of inks. However, if the pressure damper employs, e.g., a common film having a certain degree of flexibility, the water content (i.e., water vapor) of the inks permeates the film and vaporizes, and the ambient air permeates the film and becomes air bubbles in the inks, because the film directly contacts the ambient air.
Hence, there has been practiced to absorb the pressure changes of inks by using a pressure damper that employs a film having not only a flexibility but also a resistance to gas permeation, such that the film directly contacts the ambient air.
In addition, Japanese Patent No. 2,887,605 or its corresponding U.S. Pat. No. 5,030,973A discloses a pressure damper for an inkjet printer wherein the damper employs a flexible membrane (i.e., a damper film) such that the membrane defines an outer surface of the damper and is exposed to the ambient air.